Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.46   11.655%   $205.9588   $205.96   $205.95   $206.00  
  Purchase #2 $185.97   12.797%   $209.7686   $209.77   $209.75   $209.80  
  Purchase #3 $80.46   11.380%   $89.6163   $89.62   $89.60   $89.60  
  Purchase #4 $218.61   10.144%   $240.7858   $240.79   $240.80   $240.80  
  Purchase #5 $126.44   6.758%   $134.9848   $134.98   $135.00   $135.00  
  Purchase #6 $159.64   12.270%   $179.2278   $179.23   $179.25   $179.20  
  Purchase #7 $156.70   8.293%   $169.6951   $169.70   $169.70   $169.70  
  7 purchase totals = $1,112.28       $1,230.0372   $1,230.05   $1,230.05   $1,230.10